1. Field of the Invention
The invention relates to a device and method that are able to determine a degradation state of a lithium ion secondary battery, particularly, a precipitation state of lithium.
2. Description of the Related Art
In a technique described in Japanese Patent Application Publication No. 2009-199936 (JP-A-2009499936), a CPU calculates an estimated amount of dendrite precipitated inside a battery pack on the basis of charge and discharge history information that indicates a charge and discharge history of the battery pack.
In a technique described in Japanese Patent Application Publication No. 2009-063555 (JP-A-2009-063555), it is determined whether lithium is precipitated on an electrode on the basis of a change (decrease) in storage capacity of an electrical storage device (lithium secondary battery).
In a technique described in Japanese Patent Application Publication No. 2007-123207 (JP-A-2007-123207), an electrode surface is drilled in the thickness direction by irradiating an ion beam, a scanning ion microscope (SIM) image of an active material layer exposed on the drilled surface is observed, and then the performance of the electrode is evaluated on the basis of the contrast of the active material in the observed SIM image.
In the technique described in JP-A-2007-123207, it is necessary to disassemble a lithium ion secondary battery. On the other hand, in the techniques described in JP-A-2009-199936 and JP-A-2009-063555, it is possible to estimate precipitation of lithium without disassembling a lithium ion secondary battery.